Self‐assembled structures in d8‐polystyrene‐block‐polyisoprene/polystyrene blends in the weak segregation regime: SAXS and TEM study

BACKGROUND: This paper reports an investigation of the microphase‐separated morphology and phase behaviour in blends of d‐polystyrene‐block‐polyisoprene with homopolystyrene in the weak segregation regime, using small‐angle X‐ray scattering and transmission electron microscopy, as a function of composition, weight‐average molecular weight and temperature. The chain length ratio parameter r_M = M_H/M_C (where M_H and M_C are the weight‐average molecular weights of the homopolymer and corresponding block copolymer chain) was selected to encompass all possible types of mutual homopolymer/block copolymer sizes. RESULTS: In the weak segregation regime the polystyrene block chains behave as a ‘wet brush’ for r_M < 1 similarly to the intermediate and strong segregation regimes. For r_M > 1 a macroscopic phase separation occurs. The domain spacing D increases systematically in the range 0 < r_M ≤ 1 with increasing concentration of homopolymer w_P and increasing r_M regardless of the implemented specific morphology, but the slope of the periodicity D versus w_P relation is smaller than in the intermediate and strong segregation regimes. CONCLUSION: The criterion for ‘wet and dry brush’ morphologies has been applied to explain the changes in microdomain morphology during the self‐assembly process. It has been shown that the parameters r_M and χ^3/2N (where χ is the Flory–Huggins parameter and N the number of segments per chain) characterize the slope of the D versus w_P relation in the weak and intermediate segregation regimes. Copyright © 2009 Society of Chemical Industry     

Nanophase morphology and crystallization in poly(vinylidene fluoride)/polydimethylsiloxane‐block‐poly(methyl methacrylate)‐block‐polystyrene blends

An approach to achieve confined crystallization of ferroelectric semicrystalline poly(vinylidene fluoride) (PVDF) was investigated. A novel polydimethylsiloxane‐block‐poly(methyl methacrylate)‐block‐polystyrene (PDMS‐b‐PMMA‐b‐PS) triblock copolymer was synthesized by the atom‐transfer radical polymerization method and blended with PVDF. Miscibility, crystallization and morphology of the PVDF/PDMS‐b‐PMMA‐b‐PS blends were studied within the whole range of concentration. In this A‐b‐B‐b‐C/D type of triblock copolymer/homopolymer system, crystallizable PVDF (D) and PMMA (B) middle block are miscible because of specific intermolecular interactions while A block (PDMS) and C block (PS) are immiscible with PVDF. Nanostructured morphology is formed via self‐assembly, displaying a variety of phase structures and semicrystalline morphologies. Crystallization at 145 °C reveals that both α and β crystalline phases of PVDF are present in PVDF/PDMS‐b‐PMMA‐b‐PS blends. Incorporation of the triblock copolymer decreases the degree of crystallization and enhances the proportion of β to α phase of semicrystalline PVDF. Introduction of PDMS‐b‐PMMA‐b‐PS triblock copolymer to PVDF makes the crystalline structures compact and confines the crystal size. Moreover, small‐angle X‐ray scattering results indicate that the immiscible PDMS as a soft block and PS as a hard block are localized in PVDF crystalline structures. © 2019 Society of Chemical Industry     

Influence of the extrusion process on the morphology and micromechanical behavior of polystyrene‐block‐(polystyrene‐co‐butadiene)‐block‐polystyrene star block copolymer/homopolystyrene blends

The influence of the extrusion process on the morphology and micromechanical behavior of an asymmetric polystyrene‐block‐(polystyrene‐co‐butadiene)‐block‐polystyrene (SBS) star block copolymer and its blends with general‐purpose homopolystyrene (hPS) was studied with films prepared with a single‐screw extruder. The techniques used were transmission electron microscopy and uniaxial tensile testing. Unlike the pure SBS block copolymer possessing a gyroid‐like morphology, whose deformation was found to be insensitive to the processing conditions, the mechanical properties of the blends strongly depended on the extrusion temperature as well as the apparent shear rate. The deformation micromechanism was primarily dictated by the blend morphology. The yielding and cavitation of the nanostructures were the principal deformation mechanism for the blends having a droplet‐like microphase‐separated morphology, whereas cavitation dominated for the blends containing macrophase‐separated layers of polystyrene. The mechanical properties of the blends were further examined with respect to the influence of the temperature and shear rate on the phase behavior of the blends. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Nanostructured polymer blends based on polystyrene‐b‐polybutadiene‐b‐poly(methyl methacrylate) triblock copolymers modified with polystyrene and/or poly(methyl methacrylate) homopolymers

Morphologies of polymer blends based on polystyrene‐b‐ polybutadiene‐b ‐poly(methyl methacrylate) (SBM) triblock copolymer were predicted, adopting the phase diagram proposed by Stadler and co‐workers for neat SBM block copolymer, and were experimentally proved using atomic force microscopy. All investigated polymer blends based on SBM triblock copolymer modified with polystyrene (PS) and/or poly(methyl methacrylate) (PMMA) homopolymers showed the expected nanostructures. For polymer blends of symmetric SBM‐1 triblock copolymer with PS homopolymer, the cylinders in cylinders core?shell morphology and the perforated lamellae morphology were obtained. Moreover, modifying the same SBM‐1 triblock copolymer with both PS and PMMA homopolymers the cylinders at cylinders morphology was reached. The predictions for morphologies of blends based on asymmetric SBM‐2 triblock copolymer were also confirmed experimentally, visualizing a spheres over spheres structure. This work presents an easy way of using PS and/or PMMA homopolymers for preparing nanostructured polymer blends based on SBM triblock copolymers with desired morphologies, similar to those of neat SBM block copolymers. © 2017 Society of Chemical Industry     

Synthesis of poly(aryl ether sulfone)‐graft‐polystyrene and poly(aryl ether sulfone)‐graft‐[polystyrene‐block‐poly(methyl methacrylate)] through atom transfer radical polymerization

A new graft copolymers poly(aryl ether sulfone)‐graft‐polystyrene (PSF‐g‐PS) and poly(aryl ether sulfone)‐graft‐[polystyrene‐block‐poly(methyl methacrylate)] (PSF‐g‐(PS‐b‐PMMA)) were successfully prepared via atom transfer radical polymerisation (ATRP) catalyzed by FeCl₂/isophthalic acid in N,N‐dimethyl formamide. The products were characterized by GPC, DSC, IR, TGA and NMR. The characterization data indicated that the graft copolymerization was accomplished via conventional ATRP mechanism. The effect of chloride content of the macroinitiator on the graft copolymerization was investigated. Only one glass transition temperature (T_g) was detected by DSC for the graft copolymer PSF‐g‐PS and two glass transition temperatures were observed in the DSC curve of PSF‐g‐(PS‐b‐PMMA). The presence of PSF in PSF‐b‐PS or PSF‐g‐(PS‐b‐PMMA) was found to improve thermal stabilities. © 2002 Society of Chemical Industry     

Influence of the incorporation of fine calcium carbonate particles on the impact strength of polypropylene/polystyrene‐block‐poly(ethylene butene)‐block‐polystyrene blends

The Izod impact strength of two kinds of ternary composites was investigated. One consisted of polypropylene (PP), the triblock copolymer polystyrene‐block‐poly(ethylene butene)‐block‐polystyrene (SEBS), and calcium carbonate (CaCO₃) particles, and the other consisted of PP, carboxylated SEBS (C‐SEBS), and CaCO₃ particles. The mean size of the CaCO₃ particles was about 160 nm. According to scanning electron microscopy observations, the composite with SEBS showed a morphology in which SEBS domains and CaCO₃ particles were independently dispersed in the PP matrix. On the other hand, the composite with C‐SEBS showed a morphology in which CaCO₃ particles were encapsulated by C‐SEBS; that is, a core–shell structure was formed. The Izod impact strength of the composite with SEBS was higher than that of the composite with C‐SEBS and the PP/SEBS and PP/C‐SEBS binary blends. According to observations of the fractured surface, the stress‐whitened area was larger in the composite with SEBS than in the composite with C‐SEBS and the PP/SEBS and PP/C‐SEBS binary blends. The toughening mechanism of the composite, using nanometer‐sized CaCO₃ particles in combination with SEBS, was examined. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Poly(styrene‐block‐butadiene‐block‐styrene‐block‐butadiene) and poly(styrene‐block‐butadiene‐block‐methyl methacrylate) copolymers as compatibilizers in PPO–SAN blends. I. Morphology and fracture behavior

The toughness behavior of PPO–SAN blends with the modifier poly(styrene‐block‐butadiene) (SBSB) and with poly(styrene‐block‐butadiene‐block‐methyl methacrylate) copolymers (SBM) under impact loading conditions has been investigated. The observed morphology of blends compatibilized with SBM, in which the rubber phase discontinuously accumulated at the PPO–SAN interface, correlated with about 20 times higher energy dissipation up to maximum force and about seven times higher deformation capacity compared to pure PPO–SAN blends. In contrast, the fracture behavior of the SBSB‐modified blends was not as strongly dependent on the rubber content. It is especially noteworthy that although the SBM modification resulted in a strong increase in toughness of the PPO–SAN blends, no decrease in stiffness could be found with up to 15% rubber additions. The values of Young's moduli remained at the same high level of the nonmodified material. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2037–2045, 2000     

Property enhancement in polypropylene ternary blend nanocomposites via a novel poly(ethylene oxide)‐grafted polystyrene‐block‐poly(ethylene/butylene)‐block‐polystyrene toughener–compatibilizer system

Synthesis and characterization of a novel toughener–compatibilizer for polypropylene (PP)–montmorillonite (MMT) nanocomposites were conducted to provide enhanced mechanical and thermal properties. Poly(ethylene oxide) (PEO) blocks were synthetically grafted onto maleic anhydride‐grafted polystyrene‐block‐poly(ethylene/butylene)‐block‐polystyrene (SEBS‐g‐MA). Special attention was paid to emphasize the effect of PEO‐grafted SEBS (SEBS‐g‐PEO) against SEBS‐g‐MA on morphology, static/dynamic mechanical properties and surface hydrophilicity of the resultant blends and nanocomposites. It was found that the silicate layers of neat MMT are well separated by PEO chains chemically bonded to nonpolar SEBS polymer without needing any organophilic modification of the clay as confirmed by X‐ray diffraction and transmission electron microscopy analyses. From scanning electron microscopy analyses, elastomeric domains interacting with MMT layers via PEO sites were found to be distributed in the PP matrix with higher number and smaller sizes than the corresponding blend. As a benefit of PEO grafting, SEBS‐g‐PEO‐containing nanocomposite exhibited not only higher toughness/impact strength but also increased creep recovery, as compared to corresponding SEBS‐g‐MA‐containing nanocomposite and neat PP. The damping parameter of the same nanocomposite was also found to be high in a broad range of temperatures as another advantage of the SEBS‐g‐PEO toughener–compatibilizer. The water contact angles of the blends and nanocomposites were found to be lower than that of neat hydrophobic PP which is desirable for finishing processes such as dyeing and coating. © 2018 Society of Chemical Industry     

Thermal behaviour of polyethylene‐block‐poly(methyl methacrylate) block copolymer: effect of multiple heating and cooling rates versus mathematical artefact

The melting and crystallization behaviours of a polyethylene‐block‐poly(methyl methacrylate) (PE‐b‐PMMA) diblock copolymer and a PE homopolymer were investigated using multiple heating and cooling rate differential scanning calorimetry (DSC) experiments, and modelling of the crystallization kinetics and lamellar thickness distribution. This new model was first validated applying literature and experimental data. The model‐predicted morphology (n = 3.2) closely matched the spherulitic morphology (n = 3), which was determined using polarized optical microscopy. For each experimental cooling rate, the model predicted diblock copolymer crystallinity that well matched the entire DSC crystallinity curve, notably for an Avrami–Erofeev index of n = 2; and apparent crystallization activation energy that hardly varied with the cooling rates used, relative crystallinity (α), and crystallization temperature or time. This disfavours the concept of variable activation energy. The use of the right crystallization model and parameter estimation algorithm is important for addressing the mathematical artefact. Under non‐isothermal cooling, the PE‐b‐PMMA diblock copolymer, as per the model prediction, crystallized without confinement (n ≠ 1), preserving the cylindrical structure. From the characteristic shapes of the crystallization function f(α(T)) versus 1/T and crystallization rate versus α plots, the resulting T_cmax and narrow α_max range can guide the search for an appropriate crystallization model. The overall treatment illustrated in this study is not restricted to a PE homopolymer and a PE‐b‐isotactic PMMA block copolymer. It can be generally applied to crystalline homopolymers and copolymers (alternating, random and block), as well as their blends. The block copolymers and blends can be crystalline–amorphous as well as crystalline–crystalline. © 2014 Society of Chemical Industry     

Singlet oxygen generation and adhesive loss in stimuli‐responsive,fullerene‐polymer blends,containing polystyrene‐block‐polybutadiene‐block‐polystyrene and polystyrene‐block‐polyisoprene‐block‐polystyrene rubber‐based adhesives

The adhesive properties, as measured by bulk tack and peel strength analysis, were found to decrease in polystyrene‐block‐polybutadiene‐block‐polystyrene (SBS) and polystyrene‐block‐polyisoprene‐block‐polystyrene (SIS) PSA films containing common singlet oxygen generators, acridine, rose bengal, and C₆₀ fullerene, when irradiated with a tungsten halogen light in air. The addition of the singlet oxygen quencher, β‐carotene, to the C₆₀ fullerene samples was found to significantly deter the rate of adhesive loss in the fullerene‐SBS and ‐SIS PSA nanocomposites. The presence of oxygen was essential to the mechanism of adhesive loss and, in combination with the effects of singlet oxygen generators and a singlet oxygen scavenger, strongly supports a singlet‐oxygen mediated process. FTIR investigations of fullerene‐SBS and ‐SIS systems suggest the initial formation of peroxides which, upon further irradiation, lead to the generation of carbonyl‐containing compounds of a ketonic type after crosslinking. Rates of SBS and SIS C‐H abstraction were comparable and found to decrease when the high‐pressure, mercury xenon irradiation source was filtered to allow only light of λ > 390 nm. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Nanophase morphology and crystallization in poly(vinylidene fluoride)/polydimethylsiloxane‐block‐poly(methyl methacrylate) blends

A polydimethylsiloxane‐block‐poly(methyl methacrylate) (PDMS‐b‐PMMA) diblock copolymer was synthesized by the atom transfer radical polymerization method and blended with a high‐molecular‐weight poly(vinylidene fluoride) (PVDF). In this A‐b‐B/C type of diblock copolymer/homopolymer system, semi‐crystallizable PVDF (C) and PMMA (B) block are miscible due to favorable intermolecular interactions. However, the A block (PDMS) is immiscible with PVDF and therefore generates nanostructured morphology via self‐assembly. Crystallization study reveals that both α and γ crystalline phases of PVDF are present in the blends with up to 30 wt% of PDMS‐b‐PMMA block copolymer. Adding 10 wt% of PVDF to PDMS‐b‐PMMA diblock copolymer leads to worm‐like micelle morphology of PDMS of 10 nm in diameter and tens of nanometers in length. Moreover, morphological results show that PDMS nanostructures are localized in the inter‐fibrillar region of PVDF with the addition of up to 20 wt% of the block copolymer. Increase of PVDF long period by 45% and decrease of degree of crystallization by 34% confirm the localization of PDMS in the PVDF inter‐fibrillar region. © 2018 Society of Chemical Industry     

In the melt,grafting of polycarbonate onto polystyrene‐block‐poly(ethylene‐butylene)‐block‐polystyrene‐grafted‐maleic anhydride: Reactive extrusion

The use of reactions between polycarbonate (PC) and polystyrene‐block‐poly(ethylene‐butylene)‐block‐polystyrene‐ grafted‐maleic anhydride (SEBS‐g‐MAH) is a convenient way to create SEBS‐g‐PC. Grafting was realized by reactive extrusion at three temperatures using SnOct₂ or TBD catalysts. SEC analyses showed the apparition of a double distribution when the TBD was used. The mean residence time widely increased when this catalyst was used, and the rheological curves depicted a percolation effect of the SEBS nodules in the PC matrix. No explicit evolution was found with the use of SnOct₂. The thermal analyses showed the disappearance of the PC phase transition temperature. The Van Gurp‐Palmen plots confirmed the efficiency of the TBD catalyst and that 260°C was the optimal reactive extrusion temperature. POLYM. ENG. SCI., 54:2660–2668, 2014. © 2013 Society of Plastics Engineers     

Atomic force microscopy study of self‐assembly behaviors of hydrophobic poly(n‐butyl methacrylate)‐block‐polydimethylsiloxane‐block‐poly(n‐butyl methacrylate) ABA triblock copolymers

Poly(n‐butyl methacrylate)‐block‐polydimethylsiloxane‐block‐poly(n‐butyl methacrylate) (PBMA‐block‐PDMS‐block‐PBMA) ABA triblock copolymers were synthesized successfully via atom‐transfer radical polymerization using PDMS as macroinitiator. The effects of PDMS content and substrate nature on self‐assembly behaviors of PBMA‐block‐PDMS‐block‐PBMAs were systematically studied using atomic force microscopy. Two series of triblock copolymers with different molecular weights and compositions, i.e. PBMA‐block‐PDMSA12‐block‐PBMAs and PBMA‐block‐PDMSA21‐block‐PBMAs, were used, where the latter were of a higher PDMS content than the former. On silicon wafer, it was found that only spherical structures formed after annealing films spin‐coated from chloroform solutions of PBMA‐block‐PDMSA12‐block‐PBMAs. In contrast, films of PBMA‐block‐PDMSA21‐block‐PBMAs formed semi‐continuous structures. On mica wafer, it was found that ordered cylindrical pores formed after annealing films spin‐coated from chloroform solutions of PBMA‐block‐PDMSA12‐block‐PBMAs. In contrast, films of PBMA‐block‐PDMSA21‐block‐PBMAs formed isolated cylinders or worm‐like morphologies. Copyright © 2011 Society of Chemical Industry     

Novel poly(methyl methacrylate)‐block‐polyurethane‐block‐poly(methyl methacrylate) tri‐block copolymers through atom transfer radical polymerization

Poly(methyl methacrylate)‐block‐polyurethane‐block‐poly(methyl methacrylate) tri‐block copolymers have been synthesized successfully through atom transfer radical polymerization of methyl methacrylate using telechelic bromo‐terminated polyurethane/CuBr/N,N,N,N″,N″‐pentamethyldiethylenetriamine initiating system. As the time increases, the number‐average molecular weight increases linearly from 6400 to 37,000. This shows that the poly methyl methacrylate blocks were attached to polyurethane block. As the polymerization time increases, both conversion and molecular weight increased and the molecular weight increases linearly with increasing conversion. These results indicate that the formation of the tri‐block copolymers was through atom transfer radical polymerization mechanism. Proton nuclear magnetic resonance spectral results of the triblock copolymers show that the molar ratio between polyurethane and poly (methyl methacrylate) blocks is in the range of 1 : 16.3 to 1 : 449.4. Differential scanning calorimetry results show T_g of the soft segment at ?35°C and T_g of the hard segment at 75°C. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Wetting behaviour and direct observation of thermally responsive polystyrene‐block‐poly(N‐isopropylacrylamide)‐block‐polystyrene electrospun fibres in aqueous environment

Electrospun fibres of thermally responsive triblock copolymer polystyrene‐block‐poly(N‐isopropylacrylamide)‐block‐polystyrene were prepared. Fibre morphology and swelling were studied below and above the lower critical solution temperature of poly(N‐isopropylacrylamide) (PNIPAM) using cryo‐electron microscopy. Cryo‐transmission electron microscopy showed that the fibre diameter increased up to 150% after immersion in water at 20 °C. In contrast, at 45 °C the fibre diameter increased considerably less. The sessile drop technique was used to characterize temperature‐dependent wetting of fibre mats. Contact angle (θ_CA) measurements revealed that a block copolymer fibre mat changed from hydrophobic (θ_CA > 90°) to hydrophilic (θ_CA < 90°) state within seconds after applying a water droplet on it at 20 °C. At 40 °C the initial contact angle was measured to be higher (135°) and it decreased much less than at 20 °C during the first minute of measurement. We observed using scanning electron microscopy that the electrospun fibres of the block copolymer having 77 wt% of PNIPAM lost their cylindrical shape and changed from fibres to thin sheets at both 20 and 40 °C within seconds after applying water on the fibres. Fibres having 55 wt% of PNIPAM were observed to be stable in water at both 20 and 40 °C, which resulted, surprisingly, in fibre mats with the strongest effects on thermally sensitive wetting. We discuss the surprising results and the implications that the evolution of fibre surface roughness has on the long‐term wetting behaviour, demonstrating a self‐adaptable hydrophilicity/hydrophobicity nature of the fibre mats. © 2013 Society of Chemical Industry     

Film formation from polystyrene–poly(butyl acrylate‐co‐methyl methacrylate) latex blends

We have employed steady sate fluorescence (SSF) and UV‐visible (UVV) techniques to determine the film formation behavior of latex blends. Blend films were prepared from mixtures of a high‐T_g pyrene (P) labeled polystyrene (PS) latex and a low‐T_g copolymer of poly(butyl acrylate‐co‐methyl methacrylate) (BuA/MMA4). Eleven different blend films were prepared in various hard/soft latex compositions at room temperature and annealed at elevated temperatures above glass‐transition (T_g) temperature of polystyerene for 10 min. Fluorescence intensity (I_P) from P was measured after each annealing step to monitor the stages of film formation. The evolution of transparency of latex films was monitored using photon transmission intensity, I_tr. Film morphologies were examined by atomic force microscopy (AFM). A significant change occurs in both I_P and I_tr intensities at a certain critical weight fraction of hard latex (R_c = 0.3). Above R_c, two distinct film formation stages, which are named as void closure and interdiffusion processes, were seen in fluorescence data. Transparency of the films was decreased with decreasing PS content, indicating that a phase separation process occurs between PS and BuA/MMA4 phases by thermal treatment, which results in turbid films. However, below R_c, no change was observed in I_P and I_tr upon annealing, whereas transparency increased overall with increasing BuA/MMA4 ratio. We explained this result as the phase separation process between PS and BuA/MMA4 blends. These results were also confirmed by AFM pictures. Film formation stages above R_c were modeled and related activation energies were calculated. POLYM. COMPOS., 27:431–442, 2006. © 2006 Society of Plastics Engineers     

Influence of a rigid polystyrene block on the free volume and ionic conductivity of a gel polymer electrolyte based on poly(methyl methacrylate)‐block‐polystyrene

Diblock copolymers poly(methyl methacrylate)‐block‐polystyrene with three different molar ratios [poly(methyl methacrylate)/polystyrene (PS) = 1:1, 1:1.5, and 1:1.8] were synthesized by atom transfer radical polymerization and used as a polymer matrix for gel polymer electrolytes (GPEs). The positron annihilation lifetime spectroscopy was applied to determine the free‐volume behaviors of different GPEs, respectively. We illustrated that a proper PS ratio may led to the formation of a high fraction of free volume, and the influence of the PS ratio on the free‐volume fraction was caused by the different morphologies of the GPEs because of the different packing densities of the PS rigid block. The ionic conductivity was correlated with the free volume in the GPE through the study of the ionic conductivity dependence on the temperature; this followed the Vogel–Tamman–Fulcher equation. Moreover, an ionic conductive model was proposed, in which variations of the free‐volume behavior provide different ionic‐conducting abilities. Thermogravimetric analysis indicated that GPEs based on different block copolymers exhibited high liquid‐electrolyte preservation properties. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43901.     

Synthesis of amphiphilic poly(methyl methacrylate)‐block‐poly(methacrylic acid) diblock copolymers by atom transfer radical polymerization

Atom transfer radical polymerization (ATRP) of 1‐(butoxy)ethyl methacrylate (BEMA) was carried out using CuBr/2,2′‐bipyridyl complex as catalyst and 2‐bromo‐2‐methyl‐propionic acid ester as initiator. The number average molecular weight of the obtained polymers increased with monomer conversion, and molecular weight distributions were unimodal throughout the reaction and shifted toward higher molecular weights. Using poly(methyl methacrylate) (PMMA) with a bromine atom at the chain end, which was prepared by ATRP, as the macro‐initiator, a diblock copolymer PMMA‐block‐poly [1‐(butoxy)ethyl methacrylate] (PMMA‐b‐PBEMA) has been synthesized by means of ATRP of BEMA. The amphiphilic diblock copolymer PMMA‐block‐poly(methacrylic acid) can be further obtained very easily by hydrolysis of PMMA‐b‐PBEMA under mild acidic conditions. The molecular weight and the structure of the above‐mentioned polymers were characterized with gel permeation chromatography, infrared spectroscopy and nuclear magnetic resonance. Copyright © 2005 Society of Chemical Industry     

Morphology and rheological behavior of maltene–polymer blends. I. Effect of partial hydrogenation of poly(styrene‐block‐butadiene‐block‐styrene‐block)‐type copolymers

Because of the importance of the maltene–polymer interaction for the better performance of polymer‐modified asphalts, this article reports the effects of the molecular characteristics of two commercial poly(styrene‐block‐butadiene‐block‐styrene‐block) (SBS) polymers and their partially hydrogenated derivatives [poly{styrene‐block[(butadiene)_1?x–(ethylene‐co‐butylene)_x]‐block‐styrene‐block} (SBEBS)] on the morphology and rheological behavior of maltene–polymer blends (MPBs) with polymer concentrations of 3 and 10% (w/w). Each SBEBS and its parent SBS had the same molecular weight and polystyrene block size, but they differed from each other in the composition of the elastomeric block, which exhibited the semicrystalline characteristics of SBEBS. Maltenes were obtained from Ac‐20 asphalt (Pemex, Salamanca, Mexico), and the blends were prepared by a hot‐mixing procedure. Fluorescence microscopy images indicated that all the blends were heterogeneous, with polymer‐rich and maltene‐rich phases. The rheological behavior of the blends was determined from oscillatory shear flow data. An analysis of the storage modulus, loss modulus, complex modulus, and phase angle as a function of the oscillatory frequency at various temperatures allowed us to conclude that the maltenes behaved as pseudohomogeneous viscoelastic materials that could dissipate stress without presenting structural changes; moreover, all the MPBs were more viscoelastic than the neat maltenes, and this depended on both the characteristics and amount of the polymer. The MPBs prepared with SBEBS were more viscoelastic and possessed higher elasticity than those prepared with SBS. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis and thermal properties of poly(methyl methacrylate)‐poly(L‐lactic acid)‐poly(methyl methacrylate) tri‐block copolymer

Poly(methyl methacrylate)‐poly(L ‐lactic acid)‐poly(methyl methacrylate) tri‐block copolymer was prepared using atom transfer radical polymerization (ATRP). The structure and properties of the copolymer were analyzed using infrared spectroscopy, gel permeation chromatography, nuclear magnetic resonance (¹H‐NMR, ¹³C‐NMR), thermogravimetry, and differential scanning calorimetry. The kinetic plot for the ATRP of methyl methacrylate using poly(L ‐lactic acid) (PLLA) as the initiator shows that the reaction time increases linearly with ln[M]₀/[M]. The results indicate that it is possible to achieve grafted chains with well‐defined molecular weights, and block copolymers with narrowed molecular weight distributions. The thermal stability of PLLA is improved by copolymerization. A new wash‐extraction method for removing copper from the ATRP has also exhibits satisfactory results. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012